This invention generally relates to the field of stand-by uninterruptible power supplies (UPS). More particular, the invention is directed to a stand-by UPS which automatically tests its load and its battery when electric utility power is available to assure availability of power in case of power failure of the electric utility.
The present invention differs from the prior art in a number of ways, including the fact that the load and the battery are tested without losing power to the load and the battery is tested rapidly and instantaneously. The test of the present invention does not require a complete test of battery discharge time.
The current state-of-the-art in load and battery testing is reflected in the design of a typical stand-by UPS made by American Power Conversion Corp. (APC), in particular, APC's Back-Up series of products with power ratings from 250 to 600 VA. To test that the load is within the rating of the APC UPS, the design forces the operator to either unplug the UPS from the source of utility power or depress a manually operated pushbutton switch. Both of these actions will force the UPS to power the load from the internal backup battery. It is then left to the operator to determine if the load operates normally. What is normal operation is not always readily determinable. One clear indication of abnormal operation, however, is a shutdown. In such a situation, the operator crashes the load electrically. Thus, the operator assumes all the risk of misjudging the suitability of load to the APC UPS. To test the battery in the APC design, it is required to recharge the battery for over 12 hours, then disconnect the UPS from the electric utility power line and allow the UPS to discharge the battery while powering the load. It is then left to the operator to decide if the battery capacity is adequate for the application. Thus, there is no objective testing in the APC design. If the duration of the operation of the load is outside of the operator's expectations, there are numerous reasons for the cause to appear as an overload, including a bad battery charger, bad inverter, bad connections, and an exhausted battery. The operator is forced to replace the battery without having any confirmation that it is the cause of inadequate performance. Also, the operator must place the load in an inactive status to conduct the test in order to avoid possible damage to data during a sudden unexpected power interruption.
The disadvantage of the required testing in the APC UPSs is that operators forget to conduct the tests and learn of either overload or a bad battery at the worst possible time, i.e., when a utility power outage happens and the UPS can not power the load and the load crashes.